SURFACE-PLASMON-POLARITON-ENHANCED RAMAN-SCATTERING FROM SELF-ASSEMBLED MONOLAYERS OF P-NITROTHIOPHENOL AND P-AMINOTHIOPHENOL ON SILVER

Highly sensitive Raman spectroscopy using a surface plasmon polariton (SPP) was studied to improve the sensitivity level of the classical Raman scattering from adsorbates on silver surface. The Otto configuration containing a gap between a prism base and adsorbates/metal in an attenuated total reflection (ATR) method was investigated to exploit in- and out-coupling of the SPP with light: (1) the Weierstrass prism was utilized to collect whole the scattered light in the SPP cone, (2) the gap size was controlled between lambda(L)/4 and 2 lambda(L)(lambda(L): wavelength of the incident light) by observing the interference fringe. The resonance condition was not significantly affected by the dielectric properties of monolayer adsorbates. Chemisorption of p-nitrothiophenol (PNTP) and p-aminothiophenol (PATP) onto a silver surface via a sulfur atom was verified by the observation that the S-H stretching band at 2550 cm(-1) disappeared, and the marker band of a bending mode in phenyl ring around 1100 cm(-1) exclusively down-shifted by ca. 20 cm(-1) upon adsorption. Nearly the same enhancement factor of ca. 170 obtained for the different symmetry species of vibrations in PNTP and PATP is probably due to random orientation of adsorbates, which results from surface roughness of the evaporated silver films. This ATR-SPP Raman spectroscopy was applied to the electrode/electrolyte interfaces in order to study the electrochemical process of adsorbates.